1. Field of the Invention
This invention relates to an improved syringe and, more particularly, to a dual-chambered syringe having a fluid reservoir accessible to a delivery chamber upon axial displacement of a plunger.
2. Background Discussion
In many medical procedures there is a need for locally anesthetizing a large region subject to an operation or other treatment. Local administration of anesthetic may require several distinct injections in the affected area, or injection of a first volume of anesthetic at a relatively shallow depth followed by one or more further injections after advancing the hypodermic needle deeper into the tissue of the patient, or both. This successive delivery of anesthetic to varying tissue depths ensures a complete and measured numbing of all of the nerve endings in the treated region.
When delivering a large quantity of any fluid using a syringe, such as in the successive, varying depth injection method, the syringe must have a large capacity, or must be withdrawn intermittently and refilled. Large syringes are cumbersome, and it is often difficult to meter small quantities with them as the barrel has a large cross-section. Thus, even a small movement of the plunger correlates to a large fluid displacement. Even smaller syringes having volumetric graduations used to inject two or three sequential doses are difficult to meter exactly. Moreover, the smaller the diameter of the syringe, the less pressure is required to deliver the injection, and consequently, less pain. Withdrawal of the syringe from an injection site for refilling and subsequent re-injection is inconvenient and increases the chance of infection and trauma to the patient.
There have been efforts in the prior art to provide a dual-chamber syringe for storing a volume of fluid in a reservoir to be transferred into a delivery chamber, or visa versa. Typically, the fluid is ejected from the delivery chamber through a nozzle by a plunger. There are various motivations for providing dual-chamber syringes, including simply increasing the syringe capacity, providing a sterile self-contained single-use syringe, and mixing two components prior to injection, for example. Many of the known devices, however, require the injection nozzle to be plugged prior to transferring fluid between the reservoir and the delivery chamber. In other known devices, one chamber is placed in communication with another only upon relative rotation of the chamber barrels.
One dual-chamber syringe is shown in U.S. Pat. No. 553,234 issued to Finot. This syringe includes a rotatable inner chamber for selectively communicating the inner chamber with either the injection nozzle or the reservoir. Despite the benefit of a larger carrying capacity, the syringe must be manipulated with two hands to transfer fluid between chambers. Further, the syringe of Finot was not designed for successive, varying depth injections which are best accomplished rapidly and with minimum lateral movement.
Despite numerous previous dual-chamber syringe designs, all share the drawback of requiring a two-handed operation to transfer fluid between the internal chambers. There is thus a need for a dual-chamber syringe particularly suited for successive, varying depth injections which can be actuated with one hand.
The syringe of this invention has several features, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of this invention as expressed by the claims which follow, its more prominent features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled, xe2x80x9cDETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT,xe2x80x9d one will understand how the features of this invention provide its benefits, which include one-handed operation; convenience of use; larger capacity; successive, varying depth injection of anesthetic; ease of introduction of medication into dense tissue; better control of quantity of anesthetic used, thereby avoiding unnecessary tissue swelling; filtration of air introduced into syringe; the use of a single needle to give multiple injections without the need to remove the needle from the body of the patient; reduction of pain during injection because smaller diameter needles may be used; and elimination of vials holding medication, thereby reducing of likelihood contamination.
The first feature of the medical syringe of this invention is that it includes a plunger having at one end a resilient seal, and a barrel having a central longitudinal axis and a pair of opposed ends. The plunger has at an end remote from the end with the resilient seal thereon a thumb ring, and the barrel has at least one external finger rest. The barrel has at one end an ejection port and at the other end an opening. Preferably, the opening in the barrel has a porous seal which surrounds the plunger. This porous seal allows air to enter the barrel yet inhibits the flow of liquid from the chamber. The ejection port and opening are aligned with each other and disposed along the longitudinal axis.
The second feature is outer and inner telescopic tubular elements seated inside the barrel to be coaxial with the longitudinal axis. The outer tubular element is mounted in a stationary position while disposed in the barrel and the inner tubular element is movable axially within the outer tubular element. The outer tubular element and barrel form a chamber which holds a reservoir of liquid. The outer tubular element has a fluid passageway therein that allows the liquid to flow from the chamber into the inner tubular element. The inner tubular element has an end nearby the injection port with a seal thereon that has an orifice therein. This inner tubular element receives the end of the plunger with the resilient seal thereon.
The third feature is that the resilient seal fits snug within the inner tubular element to grip the inner tubular element. In response to axial movement of the plunger, the inner tubular element is moved between a first and second positions. In the first position, the seal with the orifice therein seals the injection port as the plunger is moved towards the injection port, preventing liquid in the chamber from passing into the inner tubular element and forcing any liquid in the inner tubular element through the orifice and out the injection port. In the second position, the seal with the orifice therein is moved to a retracted position away from the injection port, allowing liquid to flow from the chamber through the passageway and through the orifice into the inner tubular member.
The fourth feature is that the plunger is initially in a forward position that forces the seal with the orifice therein into engagement with the injection port to seal this port. Preferably, there is a safety seal on the plunger which is broken by movement of the plunger into a retracted position, pulling the seal with the orifice therein away from the injection port. This thereby initially fills the inner tubular element with liquid from the chamber. preferably, the barrel and inner and outer tubular elements are made of a transparent or translucent material.
In another embodiment of this invention, a back flow seal is disposed in the ejection port preventing fluid from entering or leaving said barrel through said ejection port. The back flow seal forms a distal boundary of a refill chamber within said barrel. In this embodiment, the inner tubular element has at its distal end a needle having a distal tip. In response to axial movement of the plunger, the inner tubular element moves between a first position where said distal tip of the needle is located within said refill chamber allowing fluid to be drawn through the distal tip into the inner tubular element by proximal movement of the plunger relative to the inner tubular element, and a second position where said distal tip extends through said back flow seal into the ejection port allowing fluid to be expelled through said ejection port upon distal movement of the plunger relative to the inner tubular element. Preferably, there is a safety seal on the plunger which must be broken before the plunger may move with respect to the barrel.
This invention also includes a method of giving an injection of an anesthetic into the body of a patient. This method includes the steps of
(a) providing a syringe with a reservoir that contains the anesthetic and a delivery channel which receives a plunger which when moved in one direction places the channel in communication with the reservoir and in another direction discontinues the communication and ejects anesthetic from the channel,
(b) initially introducing the anesthetic using the syringe into the body of the patient, and
(c) introducing a second dosage of the anesthetic by moving the plunger in the one direction to place the reservoir into communication with the channel and refill the channel with anesthetic and then moving the plunger in the other direction to discontinue the communication and eject anesthetic from the channel.
This invention also includes a method of giving of a medication into the body of a patient, including the steps of
(a) providing a syringe with a reservoir that contains the medication and an inner tube defining a delivery channel, said tube having a needle on one end and a plunger received in the opposite end, said plunger placing the needle in communication with the reservoir when moved in one direction and discontinuing the communication and ejecting medication from the channel when moved in another direction, and
(b) using the syringe initially to introduce the medication into the body of the patient, and
(c) introducing a second dosage of the medication by moving the plunger in the one direction to place the reservoir into communication with the needle and refill the channel with medication and then moving the plunger in the other direction to discontinue the communication and eject medication from the channel.
This invention also includes a method of injecting fluid from a syringe, including the steps of
withdrawing a plunger to displace an inner tubular element into a first position within said syringe, said tubular element having a needle thereon, the needle reversing out of a back flow seal mounted in an ejection port by movement of the tubular element into said first position,
withdrawing said plunger to displace an inner resilient seal with respect to the tubular element creating a reduced pressure within said tubular element and drawing fluid therein through said needle from a reservoir formed outside of said tubular element,
depressing said plunger to displace the inner tubular element into a second position within said syringe, said needle piercing said back flow seal to reach said ejection port by movement of the tubular element into said second position, and
depressing said plunger to displace said inner resilient seal with respect to the tubular element creating an elevated pressure within said tubular element and expelling fluid therein through said needle into said ejection port.
In these methods only one hand is used to manipulate the syringe.